Species 25-30 (7 in the flora): nearly worldwide, mainly tropical and subtropical.

Ophioglossum occurs mostly in disturbed, open, grassy habitats. It is often overlooked because of superficial resemblance to seedlings of monocotyledonous plants. The intensive and careful field studies of R.D. Thomas (W. H. Wagner Jr., C. M. Allen, and G. P. Landry 1984) have greatly extended our knowledge of adder's-tongue distributions in North America. The chromosome numbers of Ophioglossum are the highest known in all vascular plants; numbers as high as 2 n =1200+ have been reported (A.Löve et al. 1977).